Mobile machines such as wheel loaders, dozers, off-highway trucks, and other heavy equipment are used to perform many tasks. To effectively perform these tasks, the machines require an engine that provides significant torque through a transmission to one or more ground engaging devices. The transmission can include, for example, a mechanical powershift transmission, a hydrostatic transmission, an electric transmission, or a hybrid transmission (e.g., a parallel path transmission that includes a combination of technologies).
During operation of a mobile machine, it may be possible for the machine to move in a direction opposite of a desired direction that has been selected by an operator of the machine. For example, the operator may select between a forward traveling direction and a reverse traveling direction. And in some situations, even though the operator has selected the forward traveling direction, it may be possible for the mobile machine to move in the reverse traveling direction. In particular, when the mobile machine is operating on a hill and the operator has requested an insufficient amount of forward torque from the transmission, it may be possible for gravity to cause the mobile machine to overcome the requested torque and roll backwards down the hill. Uncontrolled rollback of a mobile machine may be unwanted in some applications.
One attempt to prevent uncontrolled rollback of a mobile machine is described in U.S. Patent Publication No. 2009/0127012 of Leibbrandt et al. that published on May 21, 2009 (the '012 publication). In particular, the '012 publication describes a method of machine control. The method includes detecting movement of the mobile machine in a direction opposite a desired direction of movement after release of brakes, and gradually increasing torque from an automatic transmission against the rollback direction based on the detection. The amount of torque exerted by the automatic transmission against the rollback direction does not exceed a defined maximum value, such that rollback acceleration is decreased to zero or to a positive forward creep speed.
Although the method of the '012 publication may help prevent rollback of a mobile machine, the method may be less than optimal. In particular, there may be times when machine rollback is desired and/or unavoidable. Attempting to prevent rollback in these situations may be counterproductive.
The rollback prevention system of the present disclosure solves one or more of the problems set forth above and/or other problems of the prior art.